1. Field of the Invention
The present invention relates to high permittivity ceramic compositions and, more particularly, to high permittivity ceramic compositions that can be sintered at relatively low firing temperature.
2. Description of the Prior Art
Dielectric ceramics of a barium titanate system with a permittivity of 6000 to 10000 have been used as a dielectric material for high permittivity ceramic capacitors and monolithic ceramic capacitors. These ceramic compositions have high sintering temperatures ranging from 1300.degree. to 1400.degree. C. so that they consume a large amount of energy. Also, when manufacturing monolithic capacitors with these ceramic compositions, it is required to use noble metals such as Pd and Pt as a material for internal electrodes. In general, monolithic ceramic capacitors have been manufactured by forming dielectric green sheets, screening internal electrodes on the respective green sheets, stacking and pressing the green sheets to form a monolithic body, firing the monolithic body, and then forming external electrodes on opposing ends of the sintered body so as to be connected with the respective internal electrodes. Since the internal electrodes are heated up to the sintering temperature of the dielectric materials, a material for the internal electrodes is required to have a high melting point and high chemical and physical stabilities under the sintering conditions of the dielectrics. Only the noble metals can meet these requirements. Accordingly, it is impossible to manufacture inexpensive ceramic capacitors that are small in size but large in capacitance.
It is therefore an object of the present invention to provide high permittivity ceramic compositions which have high permittivity of not less than 6000 and can be sintered at temperatures not more than 1200.degree. C.
Another object of the present invention is to provide a high permittivity ceramic composition that makes it possible to produce inexpensive monolithic ceramic capacitors of a small size and large capacitance.
According to the present invention there is provided a high permittivity ceramic composition consisting essentially of a main component expressed by the general formula: EQU (Ba.sub.1-x Me.sub.x)(Ti.sub.1-y Me'.sub.y)O.sub.3
wherein
Me is Ca and/or Sr, Me' is Zr and/or Sn, x and y are respective mole fractions of Me and Me', 0.06.ltoreq.x.ltoreq.0.14, and 0.06.ltoreq.y.ltoreq.0.14; and
a secondary component consisting essentially of 65 to 90 mol % of PbTiO.sub.3, 1 to 10 mol % of Pb.sub.5 Ge.sub.3 O.sub.11 and 1 to 30 mol % of Bi.sub.2 Ti.sub.2 O.sub.7. The secondary component is contained in the ratio of 5 to 15 parts by weight to 100 parts by weight of the main component. In other words, the content of the secondary component is 5 to 15 weight percent of the amount of the main component.